Technical Field
The present invention relates to a molding apparatus and a molding method for molding a resin molded product.
Background Art
The following methods are methods of molding a duct, which is an example of a resin molded product. Two pre-molded sheets are reheated and placed in a molten state between a pair of upper and lower molds. After this, a pressurized liquid is blown in between the two sheets, while closing and adjusting the pair of molds. Consequently, a climate control duct is formed in which the first half and the second half are joined as a single unit.
Furthermore, for example, a sheet blow molding method using a foamed resin sheet is disclosed in JP-A 2001-239824 (Patent Document 1) and JP-A 2000-289093 (Patent Document 2). In the sheet blow molding method, two thermoplastic resin sheets cut in a predetermined size in advance are heated with an infrared heater and softened. Next, the sheet is pinched-off from the mold. Then, the sheet is attached firmly to the surface of the cavity by the blowing of a pressurized fluid between the sheets. Due to this, the sheet is molded into the desired shape.
However, in the sheet blow molding method mentioned above, sheets prepared in advance in room temperature are softened during sheet blow molding by reheating it with radiant heat sources such as infrared heaters. Therefore, for example, when foamed resin sheets are used, it is difficult for the sheet to be in a uniform molten state including its internal mass. In addition to this, when compared with molten and extruded sheets, the reheated sheets contain less heat. Therefore, not only does this cause poor traceability for the sheet along the mold's cavity, but also inadequate adhesion at each pinched-off section (parting line) of the two sheets. Given this situation, it is desirable to improve the adhesion of the sheets.
Furthermore, WO 2009/157197 (Patent Document 3) is an example of the related art by the present applicant. A molding apparatus of molding a resin molded product using a molten thermoplastic resin sheet is disclosed in this document.
Further, in the molding apparatus disclosed in the above mentioned Patent Document 3, the thermoplastic resin is intermittently extruded, in a predetermined extrusion amount per unit time, from the extrusion slit with a fixed gap provided on the T-Die. This extrusion is performed at a predetermined extrusion rate, such that the molten thermoplastic resin sheet suspends downward. Then, the thermoplastic resin sheet extruded downward is passed between a pair of rollers. The thermoplastic resin sheet is compressed between these rollers by narrowing the distance between this pair of rollers. Then, by rotating the pair of rollers, the thermoplastic resin sheet is sent downward. While sending the thermoplastic resin sheet through the pair of rollers, the rotation speed of the pair of rollers is adjusted so that the transmission rate of the thermoplastic resin sheet from the pair of rollers is greater than the extrusion rate of the thermoplastic resin sheet being extruded from the extrusion slit. Thus draw-down or necking-in of the thermoplastic resin sheet is effectively prevented. As a result, the thermoplastic resin sheet is formed with uniform thickness in the extruding direction. Furthermore, draw-down is the effect in which over a period of time, the molten sheet under its own weight gets stretched, and becomes thinner toward the upper part of the sheet. Also, necking-in is the effect in which the sheet width becomes lessened by contraction of the sheet due to draw-down in the width direction.
In the molding apparatus disclosed in the above Patent Document 3, a resin molded product is formed using the thermoplastic resin sheet extruded from the T-Die. Thus, the wave effect (curtain effect) may occur in the thermoplastic resin sheet extruded from the T-Die.
If the curtain effect occurs on the thermoplastic resin sheet, even when a frame comes in contact with the lateral surface of the thermoplastic resin sheet, a gap occurs between the thermoplastic resin sheet and the frame. Thus, it becomes impossible to form a closed space between the thermoplastic resin sheet, the frame, and the surface of the cavity.
Further, JP-A-06-99474 (Patent Document 4) and JP-A-54-112965 (Patent Document 5) disclose the structure of a molding apparatus using frames. In these as well, problematic situations similar to those in Patent Document 3 could occur.